Last evening I was scheduled on DL 1688 which was A319 service from MSP to YVR scheduled to depart at 21:45. During my 3.5 layover in MSP from my first flight originating in MEM, a severe thunderstorm warning was issued at MSP advising passengers to move away from the terminal windows and to expect half dollar sized hail and winds up to 60 mph (100 kph). Around the scheduled departure time we were advised that the aircraft could not fly due to hail damage. I'm not sure if the damage on the A319 occurred while it was landing or while sitting on the tarmac, but as an aside as we landed in a CRJ 900 from MEM we did experience quite a clatter of hail on the fuselage that lasted 5 seconds or less as we were nearing MSP.

Anyway, we were advised that another aircraft had been found for us, so around 22:00 we were asked to move from gate C7 to G13. The new aircraft was an A320, so seats were reassigned and I saw a catering truck at the plane as bags were also being loaded. About an hour later we were suddenly advised by the CSR at the boarding gate that she was in touch with operations and would let us know within 5 minutes if we were changing aircraft again. A couple of minutes later she advised us to all head over to gate D3. After the collective groan from the waiting crowd, we schlepped over to gate D3 where we were quickly boarded onto another A320.

Long story short, the pilot explained to us right before push back around 00:45 that the 2nd aircraft, an A320, did not have electronic equipment that was compatible with flying over the mountains, by which I assume he meant the Rocky Mountains.

I'm really curious - what does this mean that the electronic equipment was not compatible with flying over mountains? What would have been different in the second A320 from the first one?

The aircraft could of had a discrepancy, log book write up. This write up could have affected where the aircraft could be flown. Every aircraft with a write up that can be deferred and may have restrictions placed on it until the write up is cleared and no longer flying using the Minimum Equipment List, aka MEL.